VS fare codes for bookings via AirNZ? Upgrade using AirMiles

I'm looking at booking a flight from London to Auckland (and back) and plan on doing this via the Air NZ website (because I find the Virgin website isn't great at showing options with partner airlines). What I would like to do is take the Virgin flight to Shanghai, then Air NZ to Auckland - and I would like to book economy and then use my Virgin miles to upgrade on the leg between LHR and PVG.
As we all know, Virgin only allows upgrades on certain fare classes. How can I tell what class of fare that I will get when booking via the Air NZ website? I presume that if it is an upgradeable fare class, I can then just call Virgin to make the upgrade (or maybe do it via the Virgin website). Anything else I should know about trying to implement this strategy or different approaches you'd take?
Thanks in advance
James
As we all know, Virgin only allows upgrades on certain fare classes. How can I tell what class of fare that I will get when booking via the Air NZ website? I presume that if it is an upgradeable fare class, I can then just call Virgin to make the upgrade (or maybe do it via the Virgin website). Anything else I should know about trying to implement this strategy or different approaches you'd take?
Thanks in advance
James